JP2022508889A - Acoustic transmitting antenna - Google Patents

Abstract

An acoustic antenna (ANT) intended to be equipped with a sonar, of at least two transducers (TI) placed in the center of a first longitudinal axis (AI) and stacked at least along the longitudinal axis. A first assembly and a second assembly of at least two transducers (T2) are included, each transducer having at least a radiation mode having a resonance frequency called a radiation frequency and a cavity mode having a resonance frequency called a cavity frequency. In an acoustic antenna (ANT), the transducer of the first assembly is to transmit sound waves in a first continuous frequency band that extends between at least the cavity frequency and the radiation frequency of the transducer of the first assembly. Configured, and the transducer of the second assembly is configured to transmit sound within a second continuous frequency band that extends at least between the cavity frequency and the radiation frequency of the transducer of the second assembly. The cavity frequency of the transducer in the second assembly is equal to the radiating frequency plus or minus (frI-fcI) / 10 of the transducer in the first assembly, frI is the radiating frequency of the transducer in the first assembly, and fcI is. The second assembly transducer is positioned between the first assembly transducers, and any transducer in the first assembly is second. An acoustic antenna (ANT) characterized by not being positioned between the transducers of the assembly.

Description

The present invention relates to acoustic transmit and receive antennas, particularly acoustic transmit and receive antennas in the field of low frequency and intermediate frequency systems, and methods of calibrating such antennas. The present invention is particularly applicable to, but not limited to, variable depth sonar. The present invention may also be applied to other types of sonar, such as fixed antenna sonar, protective sonar or port sonar.

Maritime platforms are equipped with an underwater sonar antenna to detect and / or find underwater objects. The sonar antenna includes a set of stacked transducers attached to the support for transmitting acoustic signals. This signal is received by a set of receivers, such as a hydrophone, arranged according to the configuration selected for the configuration of the set of transmit transducers.

Current antennas for variable depth sonar (“acoustic navigation and ranging”) transmission are manufactured according to various architectures.

A planar antenna composed of an array of basic transducers can be used. These antennas transmit sonar signals. The transducers are often of the Tompilz type, which makes them bulky and heavy. Specifically, the Tompilz transducer requires that the active element (ie, the piezoelectric, magnetostrictive, magnetostrictive material element of the antenna) be equipped with bulky mechanical components such as seismic mass in the rear, roof and sealed enclosure. do. In addition, the underwater operation of these transducers involves the provision of a hydrostatic pressure compensator, without which the underwater performance of the transducer is significantly degraded. This antenna architecture is unsuitable for low mass tow design and involves overgrowth of other elements of the system.

From the standpoint of compactness and weight, other architectures such as antennas composed of vertical arrays of compact flextental transducers are preferred. However, this type of antenna obtains the frequency bandwidth required for modern wideband sonar because their transducers are single resonant and operate in a mechanical bending mode that is inherently highly overstressed. Does not allow it to be done. Therefore, low frequencies are achieved by using mechanical bending. This antenna is compact enough to reduce the bulk and mass of the system, but has the drawback of minimizing the volume of the active material, which is detrimental to the available acoustic output and thus the acoustic level. possible. The band of these antennas remains much smaller than an octave, where one octave is a frequency range of the form [f; 2f].

Antennas consisting of vertical arrays of "slotted cylinder" type transducers are also used to achieve small and low mass antennas. This type of transducer is also based on a mechanical bending system and therefore necessarily has a frequency bandwidth equal to that of a flextental transducer. U.S. Pat. No. 9,001623 proposes its integration into a towed body, and U.S. Pat. No. 8,717,849 proposes a variant thereof. This architecture allows the manufacture of compact and lightweight antennas, but remains limited in terms of frequency band and volume of active material. To overcome this, the antenna is stretched longitudinally, where the sound energy is focused in a reduced volume of fluid, which can reduce the sonar's detection performance. Extension of the antenna in the longitudinal direction is also disadvantageous in terms of towed vehicle navigation (especially at high speeds). In addition, its integration on the towed body is complex and increases the mass of the towed body, resulting in increased operational complexity.

It is also possible to use an antenna composed of a vertical array of FFR (“Ultra-Wideband”) type compact and wideband transducers to increase the width of the transmit frequency band. This type of antenna can be on sonar towed by surface vessels. French Patent No. 2776161 gives an example. The operation of these transducers is based on the coupling of two resonant modes that allow the acquisition of bandwidth of as much as an octave. In addition, the ratio of active material is very high relative to the total mass, so it is possible to achieve high power transmissions that are favorable in terms of acoustic level. However, these antennas do not allow multiple octaves to be covered.

It is also possible to use an antenna composed of a vertical array of transducers divided into groups of at least two transducers to optimize transmission band and acoustic level (French Patent No. 3026569). ). However, as above, it is not possible to cover multiple octaves.

It is possible to combine multiple FFR transducers of different sizes to increase the useful bandwidth (International Publication No. 2015/019116), which leads to an increase in mass and thus output requirements. This complicates the system. Compared to the antenna of French Patent No. 2776161, the mass and output requirements are 2.5 to 3 times higher. In addition, this solution is limited in acoustic level due to the acoustic interaction between the various transducers, so the effect of small transducers being acoustically masked by larger transducers is observed.

U.S. Pat. No. 9,001623 U.S. Pat. No. 8717849 French Patent No. 2776161 French Patent No. 3026569 International Publication No. 2015/019116 Pamphlet French Patent No. 2776161

An object of the present invention is to overcome the above-mentioned drawbacks and limitations of the prior art. Specifically, it is an object of the present invention to provide an acoustic antenna having a wide frequency band without adversely affecting the acoustic level while following the same dimensions as in the prior art in terms of mass, bulk and output.

Accordingly, one subject of the invention is an acoustic antenna intended to be equipped with a sonar, at least one that is centered on a first longitudinal axis and at least stacked along the longitudinal axis. Includes a first set of transducers and a second set of at least two transducers, each transducer having at least one radiation mode with a resonance frequency called the radiation frequency and one cavity with a resonance frequency called the cavity frequency. In an acoustic antenna having a mode, the first set of transducers is configured to transmit sound waves in a first continuous frequency band extending between the cavity frequency and the radiation frequency of at least the first set of transducers. And the second set of transducers is configured to transmit sound within a second continuous frequency band that extends between the cavity frequency and the radiation frequency of at least the second set of transducers. The cavity frequency of the first set of transducers is approximately equal to the radiation frequency plus or minus (fr1-fc1) / 10 of the first set of transducers, fr1 is the radiation frequency of the first set of transducers, and fc1 is. , An acoustic antenna characterized by the cavity frequency of the first set of transducers.

According to some embodiments of the invention
-The first set of transducers contains at least two transducers, and the second set of transducers is placed between the first set of transducers.
-The second set of transducers is divided into subgroups, each subgroup contains at least two transducers from the second set of transducers, and the spacing between each subgroup is two transducers from the same subgroup. More than an interval between, and each subgroup has at least one cavity mode with a resonant frequency called the group cavity frequency.
-The second set contains seven transducers divided into three subgroups, the first subgroup contains two transducers, the second group contains three transducers and the third sub The group comprises two transducers, and the second subgroup is placed between the first and third subgroups.
-The group cavity frequency of at least one subgroup is equal to the radiation frequency plus or minus (fr1-fc1) / 10 of the first set of transducers, and the group cavity frequency of at least one other subgroup is the first. Equal to the cavity frequency plus or minus (fr1-fc1) / 10 of a set of transducers, fr1 is the radiation frequency of the first set of transducers, and fc1 is the cavity frequency of the first set of transducers. ,
-The antenna includes a passive element stacked along the first longitudinal axis, the passive element surrounding the second set of transducers, and the radiation frequency of the second set of transducers plus or minus 0.1 × Equal to fr2, advantageously equal to the radiation frequency of the second set of transducers plus or minus 0.05 × fr2 (where fr2 is the radiation frequency of the second set of transducers), called the radiation frequency. It has at least one emission mode having a resonance frequency and also has at least one cavity mode having a resonance frequency called a cavity frequency within the first frequency band.
-The passive element is made of a material such that the E / ρ ratio of the material is higher than that of the material forming the second set of transducers, where E is the Young's modulus of the material. And ρ are the densities of the material
-The passive element is a cylinder with a larger diameter than that of the second set of transducers.
-The transducer is an FFR ("waterless ring") transducer made of piezoelectric ceramic, magnetostrictive ceramic, or magnetostrictive ceramic.
-The first set and the second set of transducers have a circular, trapezoidal or polygonal cross section.
-The antenna contains a third set of at least two transducers stacked along K longitudinal axes parallel to the first longitudinal axis, where K is greater than 1 and the third set of transducers. , At least one cavity with a resonance frequency called cavity frequency, equal to at least one radiation mode with a resonance frequency called radiation frequency and the radiation frequency plus or minus (fr2-fc2) / 10 of the second set of transducers. Having modes, fr2 is the radiation frequency of the second set of transducers, and fc2 is the cavity frequency of the second set of transducers, and the third set of transducers is at least their cavity frequencies. It is configured to transmit sound waves in a third continuous frequency band that extends between and those radiating frequencies, where the third frequency band is at least one frequency higher than the frequencies of the first and second frequency bands. And the intersection of the first, second and third frequency bands forms a continuous frequency band.
-K longitudinal axes coincide with the first longitudinal axis,
-The antenna is at least a first shift arranged to introduce a first phase shift between the excitation signal of the first set of transducers and the excitation signal of at least a subgroup of the second set of transducers. Including the transducer
-The antenna additionally contains at least a second phase shifter arranged to introduce a second phase shift between the excitation signals of different subgroups of the second set of transducers, and-the antenna is Includes N + 1 groups of transducers of the same type and N phase shifters arranged to introduce a phase shift between the excitation signal of the first group of transducers and the excitation signal of another group. , N is an antenna greater than 1.

Another subject of the invention is in the method of calibrating an acoustic antenna according to the invention.
a. The process of exciting a first group of transducers of the same type and shorting the other transducers,
b. The process of measuring the phase of the pressure wave generated by the transducers of the first group in a long-distance field,
c. The process of exciting a second group of transducers of the same type and shorting the other transducers,
d. The process of measuring the phase of the pressure wave generated by the second group of transducers in a long-distance field,
e. A step of calculating the phase difference between the phase acquired in step b and the phase acquired in step d,
f. A method comprising the step of adjusting the phase shifter so that it introduces a phase shift equal to the phase difference calculated in step e into the excitation signal transmitted to the second group of transducers. Is.

Other features, details and advantages of the invention will become apparent by reading the description provided with reference to the accompanying drawings provided as an example.

An acoustic antenna according to the first embodiment is shown. The acoustic antenna according to the 2nd Embodiment is shown. The acoustic antenna according to each of the 3rd, 4th and 5th embodiments is shown. The acoustic antenna according to each of the 3rd, 4th and 5th embodiments is shown. The acoustic antenna according to each of the 3rd, 4th and 5th embodiments is shown. The acoustic antenna according to the sixth embodiment is shown. A calibration method according to an embodiment of the present invention is shown. FIG. 6b shows the results of a simulation using an acoustic antenna according to an embodiment of the present invention presented in FIG. 6b.

Throughout this specification, the term "cylinder" is used in a general sense and refers to a ruled surface (ie, a surface in a space composed of parallel lines) whose generatrixes are parallel to each other. In some embodiments shown in the accompanying drawings, the transducer and passive element are in the shape of an annular shape (ie, the shape of a rotating column).

FIG. 1 shows an acoustic antenna ANT according to the first embodiment. The antenna ANT is centered on the first longitudinal axis A1 and includes a first set of at least two hollow columnar transducers T1 and a second set of at least two hollow columnar transducers T2. In this first embodiment, the first set comprises two transducers T1 and the second set comprises seven transducers T2. The columnar transducers T1 and T2 are formed around the same longitudinal axis A1. Transducer T2 is placed between transducers T1 and T2 without any physical overlap. This makes it possible to avoid harmful acoustic interactions such as masking of transducer T2 by transducer T1. Each transducer (T1, T2) has at least one radiation mode having a resonance frequency called a radiation frequency and at least one cavity mode having a resonance frequency called a cavity frequency. The first set of transducers T1 is configured to transmit sound waves within a first frequency band extending at least between the cavity frequency and the radiation frequency of the transducer T1, and the second set of transducers T2 is at least. It is configured to transmit sound waves in a second continuous frequency band extending between the cavity frequency and the radiation frequency of the transducer T2. Transducers T1 and T2 have different physical dimensions, in particular the transducer T2 has a cavity frequency fc2 of a second set of transducers T2 with a radiation frequency fr1 of a first set of transducers T1 (fr1-fc1) /. It has smaller physical dimensions than the transducer T1 so that it is approximately equal with a tolerance of 10 or less (ie fc2 = fr1 ± (fr1-fc1) / 10, where fc1 is the cavity frequency of the transducer T1). .. This makes it possible to acquire a continuous transmission frequency band including frequencies in the first and second frequency bands.

The second set of transducers T2 can be subdivided into subgroups containing at least two transducers. In this first embodiment, the transducer T2 is divided into three subgroups (SG1, SG2, SG3). The first subgroup SG1 comprises two transducers T2, the second subgroup SG2 comprises three transducers T2, and the third subgroup SG3 comprises two transducers T2. Subgroup SG2 is placed between subgroups SG1 and SG3. The spacing between each subgroup (ie, between the subgroups SG1 and SG2 and between the subgroups SG2 and SG3 of this first embodiment) is greater than or equal to the spacing between the transducers T2 of the same subgroup. This allows the transducer T2 to perform more functions.

Each subgroup (SG1, SG2, SG3) has at least one cavity mode with a resonant frequency called the group cavity frequency. Specifically, when two identical annular transducers are placed one above the other at short distances with respect to the acoustic wavelengths of their cavity modes, these modes interact and their frequencies drop. (Frequency in radiation mode is unaffected). Therefore, since the transducers T2 have equal physical dimensions, it is the spacing between the transducers T2 in the same subgroup that makes it possible to correct the group cavity frequency of the subgroup.

At least one of the subgroups has a group cavity frequency (ie, fcg = fr1 ± (fr1-fc1) / 10) that is approximately equal to the radiation frequency of the first set of transducers T1 with a tolerance of (fr1-fc1) / 10 or less. Here, fcg is the group cavity frequency, fr1 is the radiation frequency of the transducer T1, and fc1 is the cavity frequency of the transducer T1. At least one other subgroup has a group cavity frequency approximately equal to the cavity frequency of the first set of transducers T1, i.e. the group cavity frequency is the cavity frequency plus or minus (fr1-fc1) of the transducer T1. ) / 10. For example, in this first embodiment, it is the transducers T2 of the first subgroup SG1 and the third subgroup SG3 that have a group cavity frequency that is approximately equal to the radiation frequency of the first set of transducers T1. It is the transducer T2 of the second subgroup SG2 that has a group cavity frequency that is approximately equal to the cavity frequency of the first set of transducers T1. Therefore, in this embodiment, the spacing between the transducers T2 in the second subgroup SG2 is smaller than the spacing between the transducers T2 in the subgroups SG1 and SG3. The radiation frequency of the transducer T2 is unaffected by the spacing of the transducers T2 within the subgroup. The use of variable axial spacing between transducers to adjust the frequency of that volume mode is known from French Patent No. 3026569 cited above.

Subgroup SG2 allows for increasing the acoustic level of transducer T1 in the vicinity of the cavity frequency of transducer T1 (ie, enhancing transmission at the lowest frequency of the first frequency band), while subgroups SG1 and SG3. Transducer T makes it possible to enhance transmission in the second frequency band by having the same cavity frequency approximately equal to the emission frequency of transducer T1.

FIG. 2 presents an acoustic antenna ANT according to a second embodiment of the present invention. The acoustic antenna ANT includes two sets of transducers (T1, T2) centered on the longitudinal axis A1 and stacked along the longitudinal axis A1. Transducer T2 is placed between transducers T1 without any physical overlap between transducers T1 and T2 and is divided into three subgroups SG1, SG2 and SG3, as shown in FIG. The group cavity frequencies of the subgroups SG1 and SG3 are approximately equal to the radiation frequency of the transducer T1, and the group cavity frequencies of the subgroup SG2 are approximately equal to the cavity frequency of the transducer T1. A passive element P1 is added to the antenna ANT to enhance the acoustic level in the cavity frequency band of the transducer T1 (ie, at the lower boundary of the first frequency band). These passive elements P1 are stacked along the longitudinal axis A1, surround a second set of transducers T2, and are placed between the first set of transducers T1. These passive elements P1 have at least one radiation mode having a resonance frequency called a radiation frequency and at least one cavity mode having a resonance frequency called a cavity frequency. The passive element P1 is a cylinder, especially a ring.

In order not to interfere with the emission mode of the transducer T2, the passive element P1 is made of a material such that the E / ρ ratio of the material is higher than that of the material forming the second set of transducers T2. E is the Young's modulus of the material, and ρ is the density of the material. It also has a radiating mode that resonates at the same frequency (ie, the radiating frequency of the passive element P1 is approximately equal to the radiating frequency of the transducer T2), while it is also possible to acquire the passive element P1 having a larger diameter than that of the transducer T2. To. The radiation frequency of the element P1 is equal to the radiation frequency of the transducer T2 plus or minus 10% of the radiation frequency of the transducer T2, that is, frp1 = fr2 ± 0.1 × fr2, where frp1 is the radiation of the passive element P1. It is a frequency, and fr2 is the radiation frequency of the transducer T2. Preferably, frp1 = fr2 ± 0.05 × fr2.

In addition, in order to prevent the transmission of the passive element P1 from masking the transmission of the transducer T2, the radiation frequency of the passive element P1 is substantially equal to the radiation frequency of the transducer T2 of the second set SG2, and the cavity of the passive element P1. The frequency is within the first frequency band.

The excitation of the passive element P1 is derived from the sound field generated by the transducer T1 and the central transducer T2 (ie, the transducer T2 of the subgroup SG2 in this embodiment).

According to another embodiment, the cavity frequency of the passive element P1 is approximately equal to the cavity frequency of the first set of transducers T1. This means that the cavity frequency of the passive element P1 is equal to the cavity frequency plus or minus (lcp1 + lc1) / 2 of the transducer T1, where lcp1 is the full width at half maximum of the cavity mode of the passive element P1 and lc1. Is the full width at half maximum of the cavity mode of the transducer T1. This allows the acoustic level in the first frequency band to be enhanced more effectively.

3a, 3b and 3c show acoustic antenna ANTs according to the third, fourth and fifth embodiments, respectively. In these three embodiments, the acoustic antenna ANT is centered on the first longitudinal axis A1 and comprises three sets of transducers T1, T2 and T3. The transducers T1 and T2 are stacked along the first longitudinal axis A1 and the transducer T3 is stacked along the second longitudinal axis A2 parallel to the axis A1. Passive elements P1, transducers T2 and T1 are arranged and dimensioned in the same manner as in FIG. Specifically, the cavity frequency of the transducer T2 is approximately equal to the radiation frequency of the first set of transducers T1, which is divided into three subgroups SG1, SG2 and SG3. The group cavity frequencies of the subgroups SG1 and SG3 are approximately equal to the radiation frequencies of the first set of transducers T1, and the group cavity frequencies of the subgroup SG2 are approximately equal to the cavity frequencies of the transducer T1. In addition, the radiation frequency of the passive element P1 is equal to the radiation frequency of the transducer T2 plus or minus 0.1 × fr2, preferably plus or minus 0.05 × fr2, where fr2 is the radiation frequency of the transducer T2. And the cavity frequency of the passive element P1 is within the first frequency band.

The third set of transducers T3 is sized to transmit sound waves in a third continuous frequency band different from the first and second frequency bands. The transducer T3 has at least one radiation mode having a resonance frequency called a radiation frequency and at least one cavity mode having a resonance frequency called a cavity frequency. The third frequency band extends at least between the cavity frequency and the radiation frequency of the third set of transducers T3. In addition, the cavity frequency of the third set of transducers T3 is approximately equal to the radiation frequency of the second set of transducers T2. Therefore, the cavity frequency of the transducer T3 is equal to the emission frequency plus or minus (fr2-fc2) / 10 of the transducer T2, where fr2 is the emission frequency of the transducer T2 and fc2 is the cavity frequency of the transducer T2. Is. Therefore, the combination of the first, second and third frequency bands makes it possible to obtain a continuous frequency band covering 3 octaves. This third frequency band is acquired for sizing the third set of transducers T3, which have smaller physical dimensions than the transducers T1 and T2.

In the embodiment shown in FIG. 3a, the longitudinal axis A2 is different from the axis A1 and therefore the transducer T3 is placed next to the structure comprising the transducers T1 and T2. This embodiment is possible because the transducers T1 and T3, which are smaller than T2, do not significantly mask other transducers.

In the embodiment shown in FIG. 3b, the antenna ANT includes a plurality of transducers T3 stacked along two longitudinal axes A2 and A3 that are parallel to the axis A1 and different from the axis A1. This is because it obtains a more compact antenna along the longitudinal axis A1 and causes omnidirectional acoustic transmission when the transducers T3 stacked along the axes A2 and A3 alternate with other transducers. Alternatively, it also makes it possible to overcome the effects of masking of transducer T3 by transducers T1 and T2 in order to produce directional acoustic transmission that is directional when all of the transducers transmit simultaneously.

More generally, the antenna ANT may include a plurality of transducers T3 stacked along K longitudinal axes parallel to axis A1, where K is an integer greater than 1. Again, more generally, the antenna ANT is a set of transducers T2, T3 ,, each containing at least one transducer. .. .. , TN can be included, each set of transducers is stacked along K longitudinal axes parallel to axis A1, on which transducers T1 are stacked, where N is an integer greater than 2.

In the embodiment shown in FIG. 3c, the longitudinal axis A2 coincides with the axis A1. The transducer T3 is placed between the transducers T2 (particularly between the subgroups SG1 and SG3), and the subgroup SG2 is replaced by the transducer T3. The spacing between the third set of transducers T3 is defined in a manner similar to transducer T2 for transducer T1 shown above. For example, in the figure, the distance between the transducer T3 and the transducers of the subgroup SG1 or SG3 is greater than the distance between the transducers T3 and also greater than the distance between the transducers T2 of the same subgroup.

More generally, when these K axes are positioned so that the radial bulk of the set of transducers T3 is about plus or minus 10% of the outer diameter of the transducer T1, they are on the towed body. A compact antenna suitable for installation is obtained. This makes it possible to realize omnidirectional and directional directional acoustic transmission by the transducers T1, T2 and T3 which are simultaneously active. In another embodiment it is possible to have K longitudinal axes that coincide with axis A1. This configuration can be used, for example, for fixed installations.

In addition, a passive element P2 may also be present to enhance the acoustic level of the transducer T2. These passive elements P2 are stacked along the longitudinal axis A1 and surround a third set of transducers T3. The passive element P1 may surround the passive element P2 as shown in FIG. 3c. The passive element P2 has at least one radiation mode having a resonance frequency called a radiation frequency and at least one cavity mode having a resonance frequency called a cavity frequency. The radiation frequency of the passive element P2 is substantially equal to the radiation frequency of the third set of transducers T3, and the cavity frequency of the passive element P2 is within the second frequency band. Similar to the above, this means that the radiation frequency of the passive element P2 is equal to the radiation frequency plus or minus 0.1 × fr3 of the transducer T3, preferably plus or minus 0.05 × fr3, where fr3 is. The radiation frequency of the transducer T3. In addition, like the passive element P1, the passive element P2 is a material and the E / ρ ratio of the material forms the transducer T3 so that it does not interfere with the radiation mode of the transducer T3 positioned around it. Made of a material that is higher than that of the material to be used, E is the Young's modulus of the material, and ρ is the density of the material.

According to another embodiment, it is also possible to subdivide the transducer T3 into subgroups to enhance the acoustic level in the lower portion of the third frequency band, such as the transducers T1 and T2.

More generally, it is possible to generate an acoustic antenna with a recursive structure. The transducers are sized so that the low frequency mode (ie, cavity mode) of the transducers of pair i + 1 is superimposed on the high frequency mode (ie, radiation mode) of the transducers of pair i + 1.

If the transducer is in single mode, the same principle can be used by matching the lowest of the transmit frequency bands of the transducers of pair i + 1 to the top of the transmit frequency band of the transducers of pair i + 1.

If the transducer is multimode, use the same principles as a dual mode transducer (ie, a transducer with cavity and radiation modes) and the highest resonant frequency of the set i transducer and the lowest resonant frequency of the set i + 1 transducer. It is possible to match.

In addition, the transducers are arranged such that the transducer operating at high frequency is inserted between at least two transducers operating at low frequency.

More generally, the number of passive elements P1 and P2 is equal to N, where N is a natural number greater than 1. Each set of subgroups may contain several M transducers, which are integers greater than 1. Thus, an acoustic antenna may include, for example, three transducers T1 each surrounding a set of, for example, transducers T2 and / or T3. In addition, the first set of transducers T1 may be placed between two transducers in another set of transducers that have a lower transmission frequency band than the transducer T1. The antenna may also include a plurality of transducers T1 divided into subgroups of at least two transducers.

FIG. 4 shows an acoustic antenna ANT according to the sixth embodiment. The physical dimensions of the antenna ANT and the spread of the frequency band covered by all of the transducers (T1, T2) or (T1, T2, T3) contained in the antenna ANT destructively interfere with some frequencies in this frequency band. Can appear, creating a "gap" within the frequency band of the antenna. This can be avoided by appropriately phase-shifting the excitation signals (preferably derived from the single generator G) of the transducers forming these various "secondary antennas". In the embodiment of FIG. 4, the first set of transducers T1 serves as a reference and is directly connected to the generator G, and the transducers T2 of the subgroups SG1 and SG3 have a phase difference of Δφ1. Connected to the generator G via a first phase shifter D1 configured to apply to the excitation signal received by, the transducers T2 of the subgroup SG2 receive the phase difference Δφ2 by these transducers. It is connected to the generator G via a second phase shifter D2 configured to be applied to the excitation signal.

According to another embodiment, the antenna ANT applies a phase difference to the excitation signals transmitted to all of the second set of transducers T2 with respect to the excitation signals transmitted to the first set of transducers T1. Includes only one phase shifter configured in.

Similarly, the antenna ANT is configured to apply a phase difference to the excitation signal transmitted to the third set of transducers T3 with respect to the excitation signal transmitted to the second set of transducers T2. May include a phase shifter.

More generally, it is possible to take any set or subgroup of transducers as a reference and then add a phase shifter to phase shift the other transducers to the reference set of subgroups. Is.

According to another embodiment, the phase shifter is adjustable.

According to one embodiment of the invention, the transducers (T1, T2, T3) are "waterless ring" (FFR) transducers. Specifically, they are made of piezoelectric ceramics, magnetostrictive ceramics or electrostrictive ceramics. Transducers can also be made of materials derived from a mixture of piezoelectrics such as single crystals or textured ceramics or materials based on various principles such as electromechanics.

According to another embodiment, the transducers (T1, T2, T3) have a circular, trapezoidal or polygonal cross section. The diameter of the transducer is defined by the longest length of the segment within its cross section.

According to another embodiment, it is possible to place at least two antenna ANTs manufactured according to the present invention adjacent to each other in order to obtain a larger transmit power and directional transmit, directional or omnidirectional transmit. Allows you to specifically increase the acoustic level in.

FIG. 5 presents a method of calibrating an acoustic antenna according to an embodiment of the present invention. In step a, the first group of transducers of the same type are excited and the other transducers are shorted. In the next step b, the phase of the pressure wave generated by the first group of transducers is measured in a long distance field. In the next step c, a second group of transducers of the same type is excited and the other transducers are shorted. In step d, the phase of the pressure wave generated by the second group of transducers is measured in a long distance field. Step e includes calculating the phase difference between the measurement results from step b and step d. Finally, in step f, the phase shifter is tuned to introduce a phase shift equal to the phase difference calculated in step e into the excitation signal transmitted to the second group of transducers.

For example, the first group of transducers is the first set of transducers T1 and the second group of transducers is the second set of transducers T2. Therefore, it would be possible to use the phase shifter D1 present in FIG. 4 to introduce into the transducer a phase shift equal to the phase difference calculated by these two groups.

In another example, the first group of transducers comprises a first set of transducers T1 and the second group of transducers comprises a subgroup SG2 transducer T2. Therefore, the phase shifter D2 present in FIG. 4 may be used to introduce a phase shift equal to the phase difference calculated by these two groups.

FIG. 6a presents the result of a simulation using an acoustic antenna according to an embodiment of the present invention (particularly, a transmitted sound level according to a frequency). In this embodiment presented in FIG. 6b, the acoustic antenna ANT includes two transducers T1 belonging to the first set and four transducers T2 belonging to the second set. Transducer T2 is not subdivided into subgroups. Many configurations of acoustic antennas have been studied. In the first configuration, only the transducer T1 is active and transmits sound waves. In the second configuration, only the transducer T2 is in the active state and transmits a sound wave, and in the third configuration, the transducers T1 and T2 are all in the active state and transmit a sound wave. Configurations 1 to 3 are generated without the use of a phase shifter. In configuration 4, the transducers T1 and T2 are all active and the phase shifter is used to apply the calibration method described in FIG.

Configuration 1 is represented by a gray dashed line curve, Configuration 2 is represented by a gray dashed line curve, Configuration 3 is represented by a black dashed line curve, and Configuration 4 is represented by a solid black-dotted curve. Finally, the solid gray curve represents the desired maximum acoustic level. If the first and second sets of transducers are not active at the same time, they will acquire an acoustic transmission with sufficient acoustic level (ie, -3 dB for the desired acoustic level) over a continuous frequency band of two octaves. It can be clearly seen that this is not possible.

If both sets of transducers are activated simultaneously (Structure 3), the transmitted sound level is increased over two octaves, but is still inadequate as it is more than 3 dB below the desired acoustic level at some frequencies. .. The use of the phase shifter according to the calibration method of Configuration 4 is greater than -3 dB with respect to the desired maximum level, so it is possible to obtain a continuous transmission frequency band of at least 2 octaves with sufficient acoustic level.

This use is here intended to be included in a variable depth sonar tow, but nevertheless, the acoustic antenna according to the invention can be installed on any carrier where protection is installed by the dome. .. It can also be used on fixed stations and therefore does not require any special protection.

Claims (16)

An acoustic antenna (ANT) intended to be equipped with a sonar, at least one transducer (T1) placed in the center of a first longitudinal axis (A1) and stacked at least along the longitudinal axis. A first set of transducers and a second set of at least two transducers (T2), each transducer having at least one radiation mode having a resonance frequency called the radiation frequency and a resonance frequency called the cavity frequency 1. In an acoustic antenna (ANT) having one cavity mode, the first set of transducers is a first continuum extending between the cavity frequency and the radiation frequency of at least the first set of transducers. The second set of transducers is configured to transmit sound waves within a frequency band, and the second set of transducers extends between the cavity frequency and the radiation frequency of at least the second set of transducers. Configured to transmit sound within the frequency band, the cavity frequency of the second set of transducers is at the radiation frequency plus or minus (fr1-fc1) / 10 of the first set of transducers. Approximately equal, fr1 is the radiation frequency of the transducers of the first set, and fc1 is the cavity frequency of the transducers of the first set, and the second set. An acoustic antenna characterized in that the transducers of the first set are placed between the transducers of the first set and no of the transducers of the first set are placed between the transducers of the second set. (ANT). The acoustic antenna according to claim 1, wherein the first set of the transducers comprises at least two transducers, and the second set of the transducers is placed between the first set of the transducers. The second set of transducers is subdivided into subgroups, each subgroup comprising at least two transducers in the second set, and the spacing between each subgroup is two transducers in the same subgroup. The acoustic antenna of claim 1 or 2, wherein the interval is greater than or equal to, and each subgroup has at least one cavity mode having a resonant frequency referred to as a group cavity frequency. The second set includes seven transducers divided into three subgroups, the first subgroup (SG1) contains two transducers, and the second subgroup (SG2) contains three transducers. 3, The third subgroup (SG3) comprises two transducers, and the second subgroup is placed between the first subgroup and the third subgroup, claim 3. The acoustic antenna described in. The group cavity frequency of at least one subgroup is equal to the radiation frequency plus or minus (fr1-fc1) / 10 of the transducer of the first set of transducers, and the group cavity frequency of at least one other subgroup. Is equal to the cavity frequency plus or minus (fr1-fc1) / 10 of the first set of the transducers, fr1 is the radiation frequency of the first set of transducers, and fc1 is the said. The acoustic antenna according to claim 3 or 4, which is the cavity frequency of the transducer of the first set. The passive element (P1) includes a passive element (P1) stacked along the first longitudinal axis, which surrounds the second set of the transducers and emits the second set of the transducers. Equal to frequency plus or minus 0.1 x fr2, and advantageously equal to the radiation frequency plus or minus 0.05 x fr2 of the second set of transducers (where fr2 is the second set of said. Also at least one cavity mode having a resonance frequency called the cavity frequency within the first frequency band, having at least one emission mode having a resonance frequency called the radiation frequency), said radiation frequency of the transducer). The acoustic antenna according to any one of claims 1 to 5. The passive element is made of a material such that the E / ρ ratio of the material is higher than that of the material forming the second set of transducers, where E is the Young's modulus of the material. The acoustic antenna according to claim 6, wherein and ρ are the densities of the materials. The acoustic antenna of claim 7, wherein the passive element is a cylinder having a diameter larger than that of the second set of transducers. The acoustic antenna according to any one of claims 1 to 8, wherein the transducer is an FFR (“waterless ring”) transducer made of piezoelectric ceramic, magnetostrictive ceramic, or magnetostrictive ceramic. The acoustic antenna according to any one of claims 1 to 9, wherein the first set and the second set of the transducers have a circular, trapezoidal or polygonal cross section. Includes a third set of at least two transducers (T3) stacked along K longitudinal axes (A2, A3) parallel to the first longitudinal axis (A1), where K is greater than 1. The third set of the transducers has at least one radiation mode having a resonance frequency called the radiation frequency and the second set of the transducers have the radiation frequency plus or minus (fr2-fc2) / 10. It has one cavity mode with a resonance frequency that is equal, called the cavity frequency, fr2 is the radiation frequency of the second set of the transducers, and fc2 is the second set of the transducers. The cavity frequency, the third set of the transducers, is configured to transmit sound waves in a third continuous frequency band extending between at least those cavity frequencies and their radiation frequencies. The frequency band 3 has at least one frequency higher than the frequency of the first and second frequency bands, and the intersection of the first, second and third frequency bands forms a continuous frequency band. The acoustic antenna according to any one of claims 1 to 10. The acoustic antenna according to claim 11, wherein the K longitudinal axes coincide with the first longitudinal axis. At least a first phase shift (Δφ1) arranged to introduce a first phase shift (Δφ1) between the excitation signal of the first set of transducers and the excitation signal of at least a subgroup of the second set of transducers. The acoustic antenna according to any one of claims 1 to 12, comprising the phase shifter (D1) of the above. Claimed, it further comprises at least a second phase shifter (D2) arranged to introduce a second phase shift (Δφ2) between the excitation signals of different subgroups of the second set of transducers. 13. The acoustic antenna according to 13. With N + 1 groups of transducers of the same type and N phase shifters arranged to introduce a phase shift between the excitation signal of said transducer in the first group and the excitation signal of another group. The acoustic antenna according to any one of claims 1 to 14, wherein N is an integer larger than 1. In the method for calibrating an acoustic antenna according to any one of claims 13 to 15.
a. The process of exciting a first group of transducers of the same type and shorting the other transducers,
b. The step of measuring the phase of the pressure wave generated by the transducer of the first group in a long-distance field.
c. The process of exciting a second group of transducers of the same type and shorting the other transducers,
d. The step of measuring the phase of the pressure wave generated by the transducer of the second group in a long-distance field.
e. A step of calculating the phase difference between the phase acquired in step b and the phase acquired in step d,
f. The phase shifter comprises adjusting the phase shift so that it introduces a phase shift equal to the phase difference calculated in step e into the excitation signal transmitted to the transducers of the second group. How to feature.

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